The present invention relates generally to vacuum pump assemblies and, more particularly, to a rotary vacuum pump having a pneumatic valve which is installed in its suction port and which is controlled by an auxiliary valve. The pneumatic valve closes the suction port of the vacuum pump in a vacuum-tight manner against an adjoining container when the vacuum pump is stationary.
Vacuum pumps of the type to which the present invention relates generally require a shutoff valve located between the working chamber of the vacuum pump and the container to be evacuated by the pump with the shutoff valve closing off in a vacuum-tight manner the flowpath between the container to be evacuated and the working chamber of the pump when the pump is stationary. Without the provision of such a shutoff valve, the container can be ventilated through the pump and, additionally, sealing fluid may be introduced into the container particularly in liquid sealed vacuum pumps.
Vacuum pumps having a pneumatic valve which is controlled by an auxiliary valve in order to close off the suction port of the pump are known in the art. In such prior art devices, the auxiliary valve is usually actuated mechanically by a centrifugal switch which is coupled with the pump shaft.
However, such pump or valve controls have the disadvantage that the pneumatic valve may allow atmospheric air to be introduced therein. The atmospheric air may intrude into the container, and this is most likely to occur particularly when the pump is restarted after having been stopped. It is very important that such an occurrence be avoided particularly in cases where the pump is to be utilized in handling toxic or expensive gases.
A further disadvantage of such pumps is the susceptibility of the centrifugal switch to malfunction or improper operation.
Auxiliary valves which operate to actuate the shutoff valve, for example, by hydraulic means, have the disadvantage that their operation may be impeded or stopped when the hydraulic fluid, normally the sealing oil contained in the pump, is mixed or loaded with gas. Problems may also arise due to a high level of temperature dependence with regard to the viscosity of the hydraulic fluid.
It is an object of the present invention to provide a vacuum pump wherein the suction port may be rapidly sealed in a vacuum-tight manner at a rotational speed below the minimum speed of the pump by means of a pneumatic valve which is controlled by an auxiliary valve. The present invention particularly aims toward providing such a device whereby the control of the auxiliary valve is independent of the power lines of the pump and is effected without additional mechanical or hydraulic switches or final control elements.